Generation of strong radial magnetic insulation fields in high power ion diodes in extraction geometrie

The efficient conversion of the electromagnetic energy delivered by the TW pulsed power generator KALIF into a high power ion beam requires a strong externally applied magnetic field which suppresses the electron flow. This pulsed insulating magnetic field is produced by two coils concentric to the beam axis and placed on the cathode side of the ion beam diode of the extraction type used in our experiments. Operating this diode with ratios of Vcrit to Vdiode >3, a field strength near the anode surface of 3 T typically had to be generated by coil currents peaking around 50 kA. With the dimensions of the coils fixed by the diodes emitting area this resulted in hoop forces up to 300 kN acting on the inner coil of just 10 cm outer diameter. The technologies developed and applied to solve the resulting mechanical, high voltage, thermal, vacuum and shock wave problems will be described. Furthermore the generated field with respect to its strength, symmetry and time response will be compared to calculations. Finally will be discussed: the influence of the insulation field strength on the ion production efficiency and the design of future field coils for higher accelerating voltages.